This disclosure relates generally to aircraft system health monitoring for overheat and fire detection systems. More particularly, this disclosure relates to aircraft system health monitoring using optical signals.
Prior art overheat detection systems typically utilize eutectic salt technology to sense an overheat event. The eutectic salt surrounds a central conductor and the eutectic salt is surrounded by an outer sheath. A monitoring signal is transmitted along the central conductor, and under normal operating conditions the eutectic salt operates as an insulator such that no conduction occurs between the central conductor and the outer sheath. When an overheat event occurs, however, a portion of the eutectic salt melts and a low-impedance path is formed between the central conductor and the outer sheath. The low-impedance path is sensed by an electronic controller, which generates an overheat alarm signal. When the overheat event has subsided, the eutectic salt re-solidifies and once again insulates the central conductor. Through the use of various salts to create a eutectic mixture, a specific melting point for the salt can be achieved. Accordingly, different eutectic salts can be used in different areas of the aircraft to provide overheat monitoring across a variety of temperatures. While the eutectic salt technology enables detection of overheat events, the eutectic salt technology merely provides a binary indication of whether an overheat event has or has not occurred.